The geometry of photocatalytic microreactors plays a critical role in determining mass transfer efficiency, particularly in three-phase (liquid–solid–gas) systems for wastewater treatment. These systems often face efficiency limits due to mass transfer challenges and heterogeneous phase distribution. This study investigates the effect of microreactor design parameters on the photocatalytic degradation of the organic dye methylene blue (MB), aiming to enhance process efficiency through geometric optimization. Seven microreactor configurations were evaluated under UV irradiation using a titanium dioxide photocatalyst with continuous oxygen injection. Performance was assessed through key indicators including the liquid-side volumetric mass transfer coefficient, space–time yield, photocatalytic space–time yield, specific removal rate, and removal efficiency. Microreactors varied in channel shape, length, and basin geometry (rhombic vs. circular, with or without a central gear). Results revealed that both basin number and shape significantly influenced mass transfer behavior. A 2.41-fold increase in removal rate was observed when the number of basins was doubled, and rhombic basins improved removal efficiency by 1.46 times compared to circular designs. In contrast, the inclusion of a central gear reduced liquid-side volumetric mass transfer coefficient by more than 30%. The most efficient design, featuring four rhombic basins, achieved 29.76% methylene blue removal, a liquid-side volumetric mass transfer coefficient of 36.4 s⁻1, a space–time yield of 8.16 × 105 mg/L·day, a photocatalytic space–time yield of 5.71 × 10–5 mg/W·day, and a specific removal rate of 2.70 × 109 mgMB/gcat·h. Process optimization using central composite design identified optimal operating conditions 0.4 mg/L TiO2, 30 ppm MB, and 20 mL/min flow rate, which resulted in high removal efficiency with residence times under one minute, a substantial improvement over conventional batch systems. The novelty of this study lies in the systematic, quantitative comparative analysis of seven distinct microreactor geometries,establishing actionable design guidelines derived from the evaluation of multiple performance indicators,which represents a substantial methodological improvement over conventional single-metric approaches. These findings demonstrate the strong potential of geometrically optimized photocatalytic microreactors for efficient and rapid wastewater treatment.

Optimization of microreactor geometry for enhanced mass transfer in three-phase photocatalytic wastewater treatment

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发表日期：

2026年6月17日

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M. Daneshvar,
A. Parvareh,
N. Azimi

摘要

The geometry of photocatalytic microreactors plays a critical role in determining mass transfer efficiency, particularly in three-phase (liquid–solid–gas) systems for wastewater treatment. These systems often face efficiency limits due to mass transfer challenges and heterogeneous phase distribution. This study investigates the effect of microreactor design parameters on the photocatalytic degradation of the organic dye methylene blue (MB), aiming to enhance process efficiency through geometric optimization. Seven microreactor configurations were evaluated under UV irradiation using a titanium dioxide photocatalyst with continuous oxygen injection. Performance was assessed through key indicators including the liquid-side volumetric mass transfer coefficient, space–time yield, photocatalytic space–time yield, specific removal rate, and removal efficiency. Microreactors varied in channel shape, length, and basin geometry (rhombic vs. circular, with or without a central gear). Results revealed that both basin number and shape significantly influenced mass transfer behavior. A 2.41-fold increase in removal rate was observed when the number of basins was doubled, and rhombic basins improved removal efficiency by 1.46 times compared to circular designs. In contrast, the inclusion of a central gear reduced liquid-side volumetric mass transfer coefficient by more than 30%. The most efficient design, featuring four rhombic basins, achieved 29.76% methylene blue removal, a liquid-side volumetric mass transfer coefficient of 36.4 s⁻¹, a space–time yield of 8.16 × 10⁵ mg/L·day, a photocatalytic space–time yield of 5.71 × 10^–5 mg/W·day, and a specific removal rate of 2.70 × 10⁹ mg_MB/g_cat·h. Process optimization using central composite design identified optimal operating conditions 0.4 mg/L TiO₂, 30 ppm MB, and 20 mL/min flow rate, which resulted in high removal efficiency with residence times under one minute, a substantial improvement over conventional batch systems. The novelty of this study lies in the systematic, quantitative comparative analysis of seven distinct microreactor geometries,establishing actionable design guidelines derived from the evaluation of multiple performance indicators,which represents a substantial methodological improvement over conventional single-metric approaches. These findings demonstrate the strong potential of geometrically optimized photocatalytic microreactors for efficient and rapid wastewater treatment.